U.S. patent application number 10/046711 was filed with the patent office on 2002-10-03 for squeezing device of a wet printer and a developing unit employing the same.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Baek, Chung-guk, Shim, Woo-jung.
Application Number | 20020141786 10/046711 |
Document ID | / |
Family ID | 19706079 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020141786 |
Kind Code |
A1 |
Shim, Woo-jung ; et
al. |
October 3, 2002 |
Squeezing device of a wet printer and a developing unit employing
the same
Abstract
A squeezing device of a wet printer for separating a liquid
carrier element that is not used for forming an image from ink
supplied to the photosensitive belt, includes a squeezing roller
mounted to be opposite to the photosensitive belt, a bias applying
unit for biasing the squeezing roller with a certain potential, and
a plurality of backup rollers mounted side by side to be opposite
to the squeezing roller across the photosensitive belt placed
between the plurality of backup rollers and the squeezing roller,
in order to extend a contact width between the photosensitive belt
and the squeezing roller. A printer to which the squeezing device
of a wet printer is applied secures a sufficient charging time of
the photosensitive belt and lowers a voltage for generating a
townsend discharge, to thereby enhance charging performances and
printing qualities.
Inventors: |
Shim, Woo-jung; (Suwon-city,
KR) ; Baek, Chung-guk; (Suwon-city, KR) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
Suite 800
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3213
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
|
Family ID: |
19706079 |
Appl. No.: |
10/046711 |
Filed: |
January 17, 2002 |
Current U.S.
Class: |
399/249 |
Current CPC
Class: |
G03G 15/11 20130101 |
Class at
Publication: |
399/249 |
International
Class: |
G03G 015/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2001 |
KR |
2001-8777 |
Claims
What is claimed is:
1. A squeezing device of a wet printer for separating a liquid
carrier element not used for forming an image from an ink supplied
to a photosensitive belt, comprising: a squeezing roller mounted to
be contacted with the photosensitive belt; a bias applying unit for
biasing the squeezing roller at a certain potential; and a
plurality of backup rollers mounted side by side to be opposite to
the squeezing roller across the photosensitive belt, the
photosensitive belt being placed between the plurality of backup
rollers and the squeezing roller.
2. The squeezing device as claimed in claim 1, wherein the
squeezing roller comprises: a core to which a bias potential is
applied to charge the photosensitive belt by the bias applying
unit; and a contact layer surrounding an outer circumference of the
core.
3. The squeezing device as claimed in claim 2, further comprising a
heater mounted in the core for heating the contact layer.
4. The squeezing device as claimed in claim 1, wherein the
squeezing roller and the plurality of backup rollers are formed to
satisfy a formula of:2R.sub.12SIN.sup.-1({fraction
(R2/R1+R2)}).gtoreq.5Rs.times.Cp- where, R.sub.1 is a radius of the
squeezing roller, R.sub.2 is a radius of the backup roller, Rs is a
resistance of the squeezing roller, and Cp is a capacitance of the
photosensitive belt.
5. A squeezing device of a wet printer for separating a liquid
carrier element not used for forming an image from an ink supplied
to a photosensitive belt, comprising: a squeezing roller mounted to
be contacted with the photosensitive belt; a bias applying unit for
biasing the squeezing roller at a certain potential; a heater for
heating the surface of the squeezing roller to a certain
temperature.
6. The squeezing device as claimed in claim 5, wherein the
squeezing roller comprises: a core to which a bias potential is
applied to charge the photosensitive belt by the bias applying
unit; and a contact layer for surrounding an outer circumference of
the core, wherein the heater is mounted in the core.
7. A developing unit of a wet printer for developing an
electrostatic latent image by supplying an ink to a photosensitive
belt, comprising: an ink supplying unit for supplying the ink to
the photosensitive belt; a squeezing roller mounted in contact with
the photosensitive belt for separating a liquid carrier element,
which is not used for forming an image, from the ink supplied to
the photosensitive belt; a bias applying unit for biasing the
squeezing roller at a certain potential; and a heater for heating
the squeezing roller.
8. The developing unit as claimed in claim 7, wherein the squeezing
roller comprises: a core to which the bias potential is applied to
charge the photosensitive belt by the bias applying unit; and a
contact layer surrounding an outer circumference of the core,
wherein the heater is mounted in the core.
9. A developing unit of a wet printer for developing an
electrostatic latent image by supplying an ink to the
photosensitive belt, comprising: an ink supplying unit for
supplying the ink to the photosensitive belt; a squeezing roller
mounted in contact with the photosensitive belt for separating a
liquid carrier element, which is not used for forming an image,
from the ink supplied to the photosensitive belt; a bias applying
unit for biasing the squeezing roller at a certain potential; and a
plurality of backup rollers mounted side by side to be opposite to
the squeezing roller across the photosensitive belt, the
photosensitive belt being placed between the plurality of backup
rollers and the squeezing roller.
10. The developing unit as claimed in claim 9, further comprising a
heater for heating the squeezing roller.
11. The developing unit as claimed in claim 10, wherein the
squeezing roller comprises: a core to which the bias potential is
applied to charge the photosensitive belt by the bias applying
unit; and a contact layer surrounding an outer circumference of the
core, wherein the heater is mounted in the core.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a squeezing device of a wet
printer and a developing unit employing the same, and more
particularly to a squeezing device of a wet printer and a
developing unit, capable of stabilizing image forming conditions
for a photosensitive medium. The present application is based on
Korean Patent Application No. 2001-8777, which is incorporated
herein by reference.
[0003] 2. Description of the Related Art
[0004] FIG. 1 is a view for schematically showing a general wet
printer.
[0005] As shown in FIG. 1, a wet printer is equipped with a
photosensitive belt 1, light scanning units 4, a transfer unit 7,
and a plurality of developing units 10.
[0006] The light scanning units 4 each scan light to the
photosensitive belt 1 charged with a certain potential to
correspond to image information. The developing units 10 are
provided for the respective colors, supply ink to the
photosensitive belt 1, and develop an electrostatic latent image
that is formed on the photosensitive belt 1 by the light scanning
units 4. The transfer unit 7 transfers a toner image formed on the
photosensitive belt 1 to supplied sheets of paper.
[0007] The developing units 10 include a container 16 for reserving
ink mixed with liquid carrier element and toner in a predetermined
ratio, developing rollers 12, ink suppliers 17 for supplying ink of
certain colors reserved in the containers 16 between the
photosensitive belt 1 and the developing rollers 12, setup rollers
13, and squeezing rollers 14.
[0008] The developing rollers are each installed to form a nip
which is a minute gap from the photosensitive belt 1, and biased
with a certain potential to fix supplied ink on an electrostatic
latent image region of the photosensitive belt 1 by an electric
force. The setup rollers 13 are installed to form a minute gap from
the photosensitive belt 1 in order to separate ink oversupplied to
the photosensitive belt 1 from the photosensitive belt 1 by the
surface tension.
[0009] The squeezing rollers 14 separate the liquid carrier element
not participating in the formation of an image from the
photosensitive belt 1 and collect the separated liquid carrier
element into a collecting reservoir 11.
[0010] A reference numeral 15 indicates backup rollers each of
which restrains the looseness of the photosensitive belt 1 and
supports the squeezing roller 14 to stably contact the
photosensitive belt 1.
[0011] As shown in FIG. 2, between the squeezing rollers 14 and the
photosensitive belt 1 are defined squeeze nips that are contact
regions for the squeezing roller 14 and the photosensitive belt 1.
Substantially, these squeeze nips may be minute gaps between the
squeezing rollers 14 and the photosensitive belt 1 which are
positioned side by side at a certain distance from each other.
[0012] The squeezing rollers 14 include a core 14a of a conductive
material and a contact layer 14b of a rubber material surrounding
the outer circumference of the core 14a. Further, the squeezing
rollers 14 can apply a bias potential to the core 14a in order to
build a condition in which another electrostatic latent image of
another color is to be formed on the photosensitive belt 1.
[0013] Ink developed on the photosensitive belt 1 has conductivity,
but the liquid carrier included in the ink is a dielectric
substance preventing electricity from flowing. However, if an
electric field stronger than a critical potential is applied to the
squeeze nips, a townsend discharge occurs so that electric currents
flow in the carrier. Accordingly, in order to charge the
photosensitive belt 1, a bias voltage over the critical potential
should be applied to the core 14a of the squeezing roller 14, which
could enable currents to flow from the squeezing rollers 14 to the
photosensitive belt 1.
[0014] The charging performance of the squeezing rollers 14 varies
with a critical potential related to the townsend discharge
occurrence, a time constant to be determined by characteristics of
the squeezing rollers 14 and the photosensitive belt 1, and a
charging time.
[0015] Meanwhile, in a conventional developing unit 10, since the
squeezing rollers 14 are supported by one cylindrical backup roller
15 and contacted with the photosensitive belt 1, the width of the
squeeze nip formed between the photosensitive belt 1 and the
squeezing roller 14 is short. The shortness of the squeeze nip
means that time required to charge the photosensitive belt 1 by the
squeezing rollers 14 is short. Accordingly, in the conventional
developing unit 10, since the charging time for the photosensitive
belt 1 is so short that the photosensitive belt 1 is not charged
with an even potential in order for an electrostatic latent image
to be formed for different colors, there exists a problem in that a
printing quality is deteriorated.
[0016] Further, in the conventional developing unit 10, since a
resistance of the contact layer 14b of each of the squeezing
rollers 14 varies with changing temperature, a critical potential
for the townsend discharge occurrence varies. Accordingly, since a
charging potential of the photosensitive belt 1 varies with
temperature, there exists a problem in that an optimum image
formation condition changes.
SUMMARY OF THE INVENTION
[0017] The present invention has been devised to solve the above
problems of the related art, and accordingly, it is an object of
the present invention to provide a squeezing device and a
developing unit employing the same, capable of securing charging
time sufficiently.
[0018] Another object of the present invention is to provide a
squeezing device that is stable with temperature changes and a
developing unit employing the same.
[0019] The above object is accomplished by a squeezing device of a
wet printer for separating a liquid carrier element not used for
forming an image from ink supplied to a photosensitive belt in
accordance with the present invention, including a squeezing roller
mounted to be contacted with the photosensitive belt, a bias
applying unit for biasing the squeezing roller at a certain
potential, and a plurality of backup rollers mounted side by side
to be opposite to the squeezing roller across the photosensitive
belt, which is placed between the plurality of backup rollers and
the squeezing roller.
[0020] The squeezing roller includes a core to which a bias
potential is applied to charge the photosensitive belt by the bias
applying unit, and a contact layer surrounding an outer
circumference of the core, and preferably further includes a heater
mounted in the core for heating the contact layer.
[0021] The above object is also accomplished by a developing unit
of a wet printer for developing an electrostatic latent image by
supplying ink to a photosensitive belt in accordance with the
present invention, including an ink supplying unit for supplying
ink to the photosensitive belt, a squeezing roller mounted in
contact with the photosensitive belt for separating liquid carrier
element, which is not used for forming an image, from the ink
supplied to the photosensitive belt, a bias applying unit for
biasing the squeezing roller at a certain potential, and a heater
for heating the squeezing roller.
[0022] Another object is accomplished by a squeezing device having
a squeezing roller mounted to be contacted with the photosensitive
belt, a bias applying unit for biasing the squeezing roller at a
certain potential, and a heater for heating a surface of the
squeezing roller at a certain temperature.
[0023] Another object of the present invention is also accomplished
by a developing unit of a wet printer for developing an
electrostatic latent image by supplying ink to the photosensitive
belt in accordance with the present invention, including an ink
supplying unit for supplying ink to the photosensitive belt, a
squeezing roller mounted in contact with the photosensitive belt
for separating liquid carrier element, which is not used for
forming an image, from the ink supplied to the photosensitive belt,
a bias applying unit for biasing the squeezing roller at a certain
potential, and a plurality of backup rollers mounted side by side
to be opposite to the squeezing roller across the photosensitive
belt, which is placed between the plurality of backup rollers and
the squeezing roller.
[0024] It is preferable that the developing unit further includes a
heater for heating the squeezing roller.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The above objects and other advantages of the present
invention will become more apparent by describing in detail a
preferred embodiment thereof with reference to the attached
drawings, in which:
[0026] FIG. 1 is a view for schematically showing a general wet
printer;
[0027] FIG. 2 is a view for showing a squeezing roller of FIG. 1 in
detail;
[0028] FIG. 3 is a view for showing a wet printer to which the
squeezing device according to an embodiment of the present
invention is applied;
[0029] FIG. 4 is a view for schematically showing the squeezing
device according to a preferred embodiment of the present
invention;
[0030] FIG. 5 is a view for showing electrical relations as to
respective constituents of the squeezing device of FIG. 4 in an
equivalent circuit diagram; and
[0031] FIG. 6 is a graph for showing a charging performance of the
squeezing device of FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0032] Hereinafter, a preferred embodiment of the present invention
will be described in detail with reference to the accompanying
drawings.
[0033] The same reference numerals are given to the same
constituents as shown in the related art, and detailed descriptions
thereof will be omitted.
[0034] FIG. 3 is a view for showing a printer to which a squeezing
device according to the present invention is applied, actually a
four-color printer enabling color printings.
[0035] As shown in FIG. 3, a printer is equipped with a
photosensitive belt 21, a plurality of light scanning units 24 and
developing units 30, a drying unit 25, and a transferring unit
27.
[0036] A reference numeral 22 denotes an eraser for erasing a
remaining electrostatic latent image by radiating light to the
photosensitive belt 21, and a reference numeral 23 is a charger for
charging the photosensitive belt 21 with a predetermined potential
in order to enable a new electrostatic latent image to be formed on
the photosensitive belt 21.
[0037] The plurality of light scanning units 24 scan the
photosensitive belt 21 with lights corresponding to image
information of four colors of yellow (Y), cyan (C), magenta (M),
and black (K) respectively. The plurality of developing units 30
supply yellow (Y), cyan (C), magenta (M), and black (K) inks to the
photosensitive belt 21 to develop an electrostatic latent image
that is formed on the photosensitive belt 21 by the light scanning
units 24. The drying unit 25 evaporates the liquid carrier element
remaining on the photosensitive belt 21. The transferring unit 27
includes a transferring roller 27a and a pressing roller 27b, and
transfers a toner image formed on the photosensitive belt 21 to
supplied sheets of paper 61.
[0038] Each developing unit 30 includes a container 36, an ink
supplier 37, a developing roller 32, a setup roller 33, and a
squeezing roller 34 and a plurality of backup rollers 35 and 36 as
a squeezing device.
[0039] Installed around the setup roller 33 and squeezing roller 34
are blades 47 and 48 that are tangentially contacted to outer
circumferences of the setup roller 33 and the squeezing roller 34,
respectively. The blade 47, which is contacted with the setup
roller 33, drops into a collecting reservoir 31 an excess of ink
that is oversupplied to the photosensitive belt 21 and collected by
the setup roller 33. The blade 48, which is contacted with the
squeezing roller 34, drops into the collecting reservoir 31 an
excess of the liquid carrier element that is oversupplied to the
photosensitive belt 21 and collected by the squeezing roller
34.
[0040] In the above structure, the setup roller 33 and the blade 47
may be omitted in case that the developing roller 32 can supply an
appropriate amount of ink to the photosensitive belt 21.
[0041] As shown in FIG. 4, a squeezing device according to the
present invention includes the squeezing roller 34, a heater
installed in the squeezing roller 34, a plurality of backup rollers
35 and 36 opposite to the squeezing roller 34, with the
photosensitive belt 21 placed between the rollers 34, 35, and 36,
and a bias applying unit 41 for applying a predetermined potential
to the squeezing roller 34.
[0042] The squeezing roller 34 includes a core 34a of a conductive
material and a contact layer 34b of a silicon substance contacted
with the photosensitive belt 21. The core 34a is electrically
connected to the bias applying unit 41, and has a cavity in which
the heater 43 can be mounted.
[0043] The heater 43 increases a temperature of the silicon layer
of the surface of the photosensitive belt 21 by increasing a
temperature of the squeezing roller 34. A heating element such as a
heat lamp can be applied as a heater 43.
[0044] The plurality of backup rollers 35 and 36 are arranged
adjacent to each other in order for a contact area of the squeezing
roller 34 and the photosensitive belt 21 to be more extended than
that of the conventional developing unit (refer to FIG. 2). That
is, by disposing the plurality of backup rollers 35 and 36, a width
Nw of a nip formed between the photosensitive belt 21 and the
squeezing belt 34 is extended more than that in the conventional
developing unit that employs one backup roller. With the nip width
Nw extended, a charging time of the photosensitive belt 21 by the
squeezing roller 34 can be more extended than that in the
conventional developing unit.
[0045] The nip width Nw can be nearly expressed as the following
formula in case that the backup rollers 35 and 36 are the same
size. 1 N w = 2 R 1 SIN - 1 ( R2 R1 + R2 ) [ Formula 1 ]
[0046] Here, R.sub.1 is a radius of the squeezing roller 34, and
R.sub.2 is a radius of the backup rollers 35 and 36.
[0047] Next, a description on charging operations of the
photosensitive belt 21 by such squeezing device will be made with
reference to FIG. 5, which is a view for showing a circuit of the
squeezing device according to the present invention.
[0048] In FIG. 5, a reference numeral dVs is a value subtracting a
potential V.sub.i of the photosensitive belt 21 prior to contacting
with the squeezing roller 34, that is, prior to charging, from a
squeeze potential Vs applied to the squeezing roller 34 by the bias
applying unit 41, and dVo is a value subtracting a potential Vi of
the photosensitive belt 21 prior to contacting with the squeezing
roller 34 from a potential Vo formed at the photosensitive belt 21
after contacting with the squeezing roller 34, that is, after
charging.
[0049] A reference numeral Rs is a resistance determined by an
electricity conductivity of the contact layer 34b of the squeezing
roller 34, and Rth is an equivalent resistance at a nip region on a
townsend discharge occurrence. Further, Vth is a critical potential
required for generating the townsend discharge, Rp is a resistance
determined by an electricity conductivity of the photosensitive
belt 21, and Cp is a capacitance of the photosensitive belt 21 of
the nip region.
[0050] Meanwhile, the charging performance of the squeezing device
is determined by the critical potential Vth, a charging time
constant, and a charging time.
[0051] In the equivalent circuit of FIG. 5, the charging time
constant becomes Rs.times.Cp.
[0052] By an experiment, in order to get a good charging
performance of the photosensitive belt 21 by the squeezing device,
it is required for a charging time to be more than five times
greater than a charging time constant.
[0053] That is, since a charging time is proportional to a nip
width Nw, the charging performance by the squeezing device becomes
good as the nip width Nw and the charging time constant satisfy the
following relationship of formula 2. 2 2 R 1 SIN - 1 ( R2 R1 + R2 )
5 R s .times. C p [ Formula 2 ]
[0054] Meanwhile, as the nip width Nw increases, the capacitance Cp
of the photosensitive belt 21 increases in proportion to the nip
width Nw, but the resistance Rs of the squeezing roller 34
decreases, so the charging time constant does not undergo a big
change.
[0055] As in Formula 2, if the nip width Nw formed by the plurality
of backup rollers 35 and 36 becomes over five times more than the
charging time constant, the charging time also becomes over five
times more than the charging time constant, so a good charging
performance can be obtained.
[0056] In the meantime, a relation between dVs, a difference value
between the squeeze potential Vs applied to the squeezing roller 34
and the potential Vi before the photosensitive belt 21 is charged,
and dVo, a difference value between a photosensitive belt potential
Vo after being charged by the squeezing roller 34 and a
photosensitive belt potential Vi before charging is as follows.
[0057] [Formula 3]
dVo=(dVs-V.sub.th)(1-e.sup.-t/.tau.)=(dVs-V.sub.th)(1-e.sup.-(Nw/Vp)/.tau.-
)
.tau.=Rs.times.Cp
[0058] Here, Vp denotes a rotation speed of the photosensitive belt
21, t denotes a charging time, and .tau. denotes a charging time
constant. In the meantime, the difference value dVo between the
photosensitive belt potential Vo after being charged by the
squeezing roller 34 and the photosensitive belt potential Vi before
charging indicates an output voltage in the equivalent circuit of
FIG. 5.
[0059] FIG. 6 is a graph for showing results obtained from
experiments of a charging performance of the squeezing device
according to the present invention.
[0060] As shown in FIG. 6, in case that a charging time to is five
times larger than a charging time constant .tau., the values of dVo
are nearly identical to the values of dVs. Accordingly, a potential
difference between the image and non-image regions on the
photosensitive belt 21 after charging becomes so small that the
photosensitive belt 21 is evenly charged. Therefore, a reset state
capable of forming a new electrostatic latent image can be
provided.
[0061] In the squeezing device according to the present invention,
the squeezing roller 34 removes carrier that is oversupplied to the
photosensitive belt 21 and charges the photosensitive belt 21 by a
bias applied by the bias applying unit 41, to thereby effectively
enable the formations and developments of electrostatic latent
images of different colors to be enabled.
[0062] In the meantime, if heat generated by the heater 43 is
transmitted to the photosensitive belt 21 through the squeezing
roller 34, a thermionic electron emission in the photosensitive
belt 21 is activated, so the critical potential Vth for charging
can be lowered.
[0063] A description on a function of the heater 43 is made in
greater detail.
[0064] In general, the critical potential Vth at which the townsend
discharge occurs is affected by temperatures. In a state in which a
temperature of the surface (for example, a silicon layer) of the
photosensitive belt 21 is low, the critical potential Vth becomes
larger since the thermionic electron emission is not easy. Further,
in a state that temperatures of ink and photosensitive belt 21 have
risen higher due to operation of a printer for a long time, the
critical potential Vth decreases since the thermionic electron
emission from the surface of the photosensitive belt 21
increases.
[0065] That is, the higher the temperature of the silicon layer
constituting the surface of the photosensitive belt 21, the lower
the critical potential Vth becomes, since the thermionic electron
emission of the silicon layer are facilitated. As a result, the
townsend discharge occurs by a low electric field.
[0066] In the case that the heater 43 does not operate, the
photosensitive belt 21 absorbs thermal energy from the transferring
roller 27b that has the surface temperature maintained at about
100.degree. C., and emits heat to supplied ink, passing through the
developing units 30 of yellow (Y), cyan (C), magenta (M), and black
(K) in order. Accordingly, the critical potential Vth upon charging
becomes about 35V for the developing unit 30 for developing the
yellow (Y) ink, about 80V for the developing unit 30 for developing
the cyan (C) ink, and about 200V for the developing unit 30 for
developing the magenta (M) ink. A reason for gradually increasing
the critical potential Vth is because the temperature of the
photosensitive belt 21 gradually falls.
[0067] However, if the heater 43 operates, through the surface of
the squeezing rollers 34, that is, through the contact layers 34b,
thermal energy is transferred to the surface of the photosensitive
belt 21 so that the thermionic electron emission from the surface
of the photosensitive belt 21 is facilitated, and the critical
potential Vth becomes much lower. That is, by constantly
maintaining the surface temperature of the photosensitive belt 21
with the operation of the heater 43, it is possible to reduce the
critical potential below 40V regardless of the kind of the
developing units 30.
[0068] The charging performance improves with lowering of the
critical potential Vth. By experiments, in case of heating and
maintaining the squeezing rollers 34 at 45.degree. C., the charging
efficiency is improved from 52% to 56%.
[0069] Further, by mounting the heater 43 to each of the squeezing
rollers 34, since thermal energy generated from the heater 43 is
transferred to the photosensitive belt 21, an evaporation rate of
the carrier goes up and the squeezing efficiency increases and the
drying load of the drying unit 25 is decreased.
[0070] As described above, with the squeezing device of a wet
printer and a developing unit 30 employing the same according to
the present invention, by securing a charging time of the
photosensitive belt 21 sufficiently and enhancing the charging
performance with lowering of a critical potential Vth for
generating a townsend discharge occurrence, the printing quality
can be enhanced.
[0071] Although the preferred embodiment of the present invention
has been described, it will be understood by those skilled in the
art that the present invention should not be limited to the
described preferred embodiment, but various changes and
modifications can be made within the spirit and scope of the
present invention as defined by the appended claims.
* * * * *